The invention relates to a colour display tube comprising an envelope consisting of a neck, a cone and a flat or slightly convex display window which changes into a skirt which is substantially parallel to the axis of the envelope via a strongly curved part, the inner surface of the display window changing into the inner surface of said skirt via a first strongly curved surface having a radius of curvature r and the outer surface of the display window changing into the outer surface of said skirt via a second strongly curved surface, the skirt, in the proximity of said transition, having a thickness d, the display window comprising on its inside a substantially rectangular display screen which comprises a material luminescing in at least one colour, colour selection means being positioned in front of said display screen by means of suspension means fixed in the skirt, means being provided in said neck to generate at least one electron beam.
The invention furthermore relates to a display device having such a display tube.
Recent developments of display tubes go more and more towards flatter display windows, as described for example, in Journal of Electronic Engineering, August 1982, p. 24. In said publication it concerns a colour display tube having a substantially rectangular display screen, in which, however, the outer contour of the display window is slightly barrel-shaped.
In colour display tubes it is usual to fix the suspension means for the colour selection means in the long and short sides of the skirt of the display window. The suspension means usually consist of metal pins which are sealed in the skirt and which each extend in an aperture of metal resilient strips connected to the colour selection means. Said metal strips are connected to a skirt of the colour selection means which also extends substantially parallel to the axis of the envelope. It will be obvious that for such a suspension construction quite some space is necessary between the skirt of the display window and the skirt of the colour selection means. For this reason, the inner contour of the skirt of the display window is constructed so as to be slightly more barrel-shaped than the contour of the skirt of the colour selection means. For tubes which are placed in a cabinet and the outer circumference of which is screened from the viewer by a fillet, this need not be an objection because the inner edge of the fillet may adjoin the edge of the display screen. However, for tubes the display window of which projects slightly beyond the cabinet (so-called push-through mounting) and the fillet can hence not be used, the substantially rectangular display screen on the inner wall of the much less rectangular display window leads to dark areas above and below and on the left and on the right of the display picture, which areas vary in width and are annoying to the viewer. This undesired effect is even more intensified by the fact that the outer contour of the display window and hence the outer contour of the skirt of the display window, in itself is constructed to be more barrel-shaped than the inner contour of the skirt of the display window. This design is assumed to be necessary in connection with the stringent requirements as regards implosion safety for the tube.